1. Field of the Invention
This invention relates to a polymer and a chemically amplified positive resist composition containing the same. More particularly, it relates to a polymer which is blended as a base resin with resist components to form a chemically amplified positive resist composition which has significantly improved alkali dissolution rate contrast before and after exposure, high sensitivity, and high resolution and is thus suitable as a fine pattern-forming material in the manufacture of ultra-LSI's.
2. Prior Art
As the LSI technology tends toward higher integration and higher speed, further refinement of pattern rules is required. Under the circumstances, deep-ultraviolet lithography is regarded promising as fine patterning technology of the next generation. The deep-UV lithography is capable of working on the order of less than 0.5 .mu.m. If a less light absorbing resist is used, it is possible to form a pattern having a side wall nearly perpendicular to the substrate.
There were recently developed positive working resist materials which undergo acid-catalyzed chemical amplification as disclosed in Japanese Patent Publication (JP-B) No. 27660/1990 (corresponding to U.S. Pat. No. 4,491,628) and Japanese Patent Application Kokai (JP-A) No. 27829/1988 (corresponding to EP 249139). Because of many advantages including sensitivity, resolution, and dry etching resistance, the chemically amplified resist materials are regarded promising for deep-ultraviolet lithography using a high intensity KrF excimer laser as a source of deep-ultraviolet radiation.
Known chemically amplified positive working resist materials include a two-component system comprising a base polymer and a photoacid generator and a three-component system comprising a base polymer, a photoacid generator, and a dissolution regulator having an acid labile group. For example, JP-A 115440/1987 (corresponding to U.S. Pat. No. 4,603,101) discloses a resist composition comprising poly-4-tert-butoxystyrene and a photoacid generator. There are proposed analogous resist compositions. JP-A 223858/1991 (corresponding to U.S. Pat. No. 5,252,435) discloses a two-component resist composition comprising a resin having a tert-butoxy group in a molecule and a photoacid generator. JP-A 211258/1992 discloses a two-component resist composition comprising a polyhydroxystyrene having a methyl, isopropyl, tert-butyl, tetrahydropyranyl or trimethylsilyl group and a photoacid generator. Further, JP-A 100488/1994 (corresponding to U.S. Pat. No. 5,324,804) discloses a resist composition comprising a polydihydroxystyrene derivative such as poly(3,4-bis(2-tetrahydropyranyloxy)styrene), poly(3,4-bis(tert-butoxycarbonyloxy)styrene), and poly(3,5-bis(2-tetrahydropyranyloxy)styrene) and a photoacid generator.
These resist compositions, however, are not necessarily satisfactory in that some are low in contrast of a dissolution rate of a resist film, some have unsatisfactory sensitivity and resolution, and some are less process adaptable. None of them have been used in practice. There is a need to overcome these problems.